There are two main types of shuttlecocks, those in which the flared skirt is made of feathers and those in which the flared skirt is made of artificial material: the former spin more rapidly than the latter when propelled at the same speed. Slow spin has been induced in shuttlecocks having a skirt of artificial material by introducing into the plane of the outer skirt deflectors such as flutes made by indenting the ribs, setting the stems at an angle to the line of flight, and similar features. Examples of specifications which have given attention to these features are GB 689532, GB907700 and D 344938. Diagrammatic sketches of well-known models from the period 1960 to 1998 are given in FIGS. 1-5 of this specification: FIG. 1 on sale by Carlton, 1960. FIG. 2 on sale by Dunlop Carlton, 1997. FIG. 3 on sale by Yonex, 1998. FIG. 4 on sale by R. J. Classic, 1998. FIG. 5 on sale by Yonex, 1998. All of these shuttlecocks incorporate flutes which are arranged in substantially the same manner as that shown in FIG. 6 and all the ribs are arranged between the stems. Projections from the outermost rib have their outermost part above the stems. Shuttlecocks having ribs between the stems but no flutes were on sale by Carlton in 1951.
Technical Problems to be Overcome
There are two problems which are associated. The first is the turnover, which is defined for the purpose of this specification as resistance to tumbling, cap over skirt, when the direction of flight is changed in play. A good turnover is aided by increasing the flare, increasing the resistance and/or reducing the weight of the outer part of the skirt. The second problem is that Law 3.1 of badminton includes the requirement that the correct speed of a shuttle is ascertained by striking a shuttle with a full underhand stroke but Law 2.1 requires that the flight characteristics should be similar to those produced by a natural feathered shuttle; these two laws are to some extent, conflicting. A full underhand stroke strikes the shuttlecock with much less force than a severe smash but a good feather shuttlecock moves quickly when smashed and decelerates rapidly immediately after the smash. This deceleration is affected by the speed of the spin of the feather shuttlecock, which is caused by the passage of air between the overlapping parts of the feathers. The technical problem is to improve the turnover and at the same time, increase the speed of the spin of a shuttlecock having a skirt made of artificial material.